In a semiconductor manufacturing process, a liquid crystal panel manufacturing process, and others, when a hot gas, such as H2 gas and Ar gas, heated to about 200° C. is to be supplied to a semiconductor manufacturing device and others or shut off, a metal diaphragm valve as disclosed for example in Patent Documents 1 and 2 is used as a fluid control valve for controlling the flow of the hot gas.
FIGS. 6 and 7 are views to explain a metal diaphragm valve of Patent Document 1. Patent Document 1 discloses, as shown in FIGS. 6 and 7, a metal diaphragm valve 201 including a metal diaphragm 260 made with a Vickers hardness of 500 Hv or more by an age-hardening heat treatment. The diaphragm 260 is configured to contact with or separate from a valve seat 250 when pressured or released by a valve rod 230. In this metal diaphragm valve 201, when the pressure of the valve rod 230 is released, the metal diaphragm 260 elastically returns to its original shape.
In Patent Document 1, the metal diaphragm 260 is hardened to a Vickers hardness of 500 Hv or more. Accordingly, even in an environment that the metal diaphragm valve 201 is heated to a high temperature, it is possible to prevent a decrease in reactive force from the valve seat 250 to the diaphragm 260 at the time of valve closing and thermal expansion of the diaphragm 260 during valve opening. Even though Patent Document 1 does not disclose any shapes, any materials, any structures, etc. of the valve seat 250, it discloses that the diaphragm 260 made with hardness can keep a gap α between the diaphragm 260 and the valve seat 250 constant during control of the flow of hot gas.
FIGS. 8 and 9 are views to explain a metal diaphragm valve of Patent Document 2. Patent Document 2 shows a metal diaphragm valve 301 including a circular metal diaphragm 360 configured to contact with or separate from a valve seat 350 when the diaphragm 360 is pressed by or released from a stem 366 through a diaphragm holding member 365 as shown in FIGS. 8 and 9. The metal diaphragm 360 is a metal thin sheet made of stainless thin sheets and cobalt alloy thin sheets in a lamination configuration and formed into a reversed dish-like shape having a central portion protruding upward. The valve seat 350 is made of synthetic resin such as PFA and fixed in a valve attachment groove of a body 340 by crimping or caulking.
Patent Document 2 discloses, as shown in FIG. 9, that a gap ΔS between the diaphragm holding member 365 and the valve seat 350 is set to a height corresponding to about 55% to 70% of a maximum protruding height Δh of the central portion of the metal diaphragm 360 from the valve seat 350. Thus, the Cv value of the metal diaphragm valve 301 can be 0.55 to 0.8.
Although no related art is cited here, there is also a metal diaphragm valve in which a ring-shaped valve seat member made of synthetic resin such as PFA is fixed in a valve attachment groove of a body by crimping or caulking in a similar manner to Patent Document 2. FIG. 10 shows the shape of this valve seat member and is an enlarged view corresponding to a part A in FIG. 1 mentioned later.
In this metal diaphragm valve, as shown in FIG. 10, assuming that the thickness of a valve seat portion 151, which a valve element will contact with and separate from, in a radial direction CR of a valve seat member 150 is a first thickness t1, the valve seat member 150 has a second thickness t2 in its height direction AX larger about 2.7 times the first thickness t1. In this metal diaphragm valve, when a valve closed state is established, the valve element (not shown) deeply presses against the valve seat member 150 and reliably comes into close contact with the valve seat member 150. Thus, a sealing performance between the valve element and the valve seat member 150 can be enhanced.